electric motor


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to electric motor: Electric generator

motor, electric,

machine that converts electrical energy into mechanical energy. When an electric current is passed through a wire loop that is in a magnetic field, the loop will rotate and the rotating motion is transmitted to a shaft, providing useful mechanical work. The traditional electric motor consists of a conducting loop that is mounted on a rotatable shaft. Current fed in by carbon blocks, called brushes, enters the loop through two slip rings. The magnetic field around the loop, supplied by an iron core field magnet, causes the loop to turn when current is flowing through it. In an alternating current (AC) motor, the current flowing in the loop is synchronized to reverse direction at the moment when the plane of the loop is perpendicular to the magnetic field and there is no magnetic force exerted on the loop. Because the momentum of the loop carries it around until the current is again supplied, continuous motion results. In alternating current induction motors the current passing through the loop does not come from an external source but is induced as the loop passes through the magnetic field. In a direct current (DC) motor, a device known as a split ring commutator switches the direction of the current each half rotation to maintain the same direction of motion of the shaft. In any motor the stationary parts constitute the stator, and the assembly carrying the loops is called the rotor, or armature. As it is easy to control the speed of direct-current motors by varying the field or armature voltage, these are used where speed control is necessary. The speed of AC induction motors is set roughly by the motor construction and the frequency of the current; a mechanical transmission must therefore be used to change speed. In addition, each different design fits only one application. However, AC induction motors are cheaper and simpler than DC motors. To obtain greater flexibility, the rotor circuit can be connected to various external control circuits. Most home appliances with small motors have a universal motor that runs on either DC or AC. Where the expense is warranted, the speed of AC motors is controlled by employing special equipment that varies the power-line frequency, which in the United States is 60 hertz (Hz), or 60 cycles per second. Brushless DC motors are constructed in a reverse fashion from the traditional form. The rotor contains a permanent magnet and the stator has the conducting coil of wire. By the elimination of brushes, these motors offer reduced maintainance, no spark hazard, and better speed control. They are widely used in computer disk drives, tape recorders, CD drives, and other electronic devices. Synchronous motors turn at a speed exactly proportional to the frequency. The very largest motors are synchronous motors with DC passing through the rotor.

Electric Motor

 

a machine that converts electrical energy into mechanical energy. The electric motor is a basic type of motor used in industry, transportation, homes, and elsewhere. Electric motors can be classified by the kind of current used for their drive. The DC motors have the advantage of an economical and smooth regulation of their rotational speed (rpm). The AC motors include synchronous and asynchronous electric motors. In a synchronous motor the rotational speed (rpm) is rigidly dependent on the frequency of the feeder current. In an asynchronous motor the rotational speed decreases as the load increases. A third type of alternating current motor is the commutator motor, which permits a smooth regulation of rotational speed within wide limits.

The asynchronous motor is the most widely used; it is simple to manufacture and is reliable in operation (particularly the squirrel-cage motors). Their main disadvantages are a considerable consumption of reactive power and the lack of a smooth (gradual) speed regulation. In many high-power electric drives, synchronous electric motors are being used. DC motors are utilized if speed regulation is of paramount importance; the more expensive and less reliable AC commutator motors are very occasionally used in these cases. The power rating of electric motors ranges from a fraction of a watt to dozens of megawatts. Electric motors have various forms of frame construction: open frame, in which the rotating and current-carrying parts are protected against accidental touching and foreign objects; protected frame (including drop-proof and spray-proof designs); closed frame (dust-proof and moisture-proof); hermetic frame; and explosion-proof frame (in case of an explosion of gases inside the motor, any flame is confined to the interior of the motor housing).

electric motor

[i¦lek·trik ′mōd·ər]
(electricity)
References in periodicals archive ?
The model is to be equipped with an 80 kW electric motor, allowing for a large improvement in acceleration speeds.
shocks from the electric motor pump as she was washing clothes near it,' they said, adding that resultantly, she received burn wounds.
In addition, stringent electricity consumption and environment protection and rising electricity prices, are forcing households across the world to replace their less efficient electric motor driven systems (EMDS) with high energy efficient electric motor driven systems.
Growth in the number of power plants and oil rigs, coupled with rapid commercialisation and urbanisation are also boosting demand for electric motors in the kingdom," it stated.
Growth in number of power plants and oil rigs, coupled with rapid commercialisation and urbanization are also boosting demand for electric motors in the Kingdom, according to the TechSci Research report.
Aging infrastructure of water and wastewater treatment facilities in North America is expected to influence the electric motor sales market growth in the coming years.
By choosing the right grease, companies may significantly reduce their annual operating costs, improve bearing performance, increase protection for long electric motor life and increase their overall productivity.
If specified, installed and maintained correctly, there is no reason why a modern electric motor should fail.
s diesel engine and electric motor each produce up to 35KW, while the maximum system power output of the Twin Up
Regional electric motor demand is expected to climb 7.
Earlier this month, the US Department of Justice (DOJ) demanded that RBC should sell the particular division to SNTech in order to conclude its acquisition of AO Smitha[euro](tm)s (NYSE:AOS) own electric motor business for USD875m (EUR605.
Among the alternatives that such companies are turning to are electric motors, which in today's business climate can offer a number of advantages: